Servomotor and control apparatus therefor



Feb. 3, 1942. I H. J. NATHAN 2,272,095

' S;ERV0M0TOR AND, CONTROLAPPARATUS THEREFOR Filed Jul 2a, 1938 Aiiorneys' Patented Feb. 3 1942 SERVO MOTOR AND CONTROLJAFPARAAT-US EFQB a J Herbert J. Nathan; Bismarck NrDak. I) I a Application; July 28, 1938,} fse ihj d z2'L's1v 3 Claims. (01.; lei-+3 My' inventionrelates to fluid pumps and particularly to control apparatus for fluid pumps which are adjusti'vely variable in capacity.

In hydraulic transmission systems for motor vehicles wherein fluid is p circulated through v wheel-driving fluid motorsbya fluid pump driven by an internal combustion engine, it isv highly desirable that the fluid pump be conveniently adjustable in capacity to provide for variation of the transmission ratio between the internal combustion engine and the wheels of the vehicle. An object of my. invention is to'providecontrol' Fig, 41, is fiakh'oriz ontal sectional view of a detail I of :my'controllapparatus and in dotted lines.

apparatus for a'fluid pump of a type which. is,

conveniently adjustable in capacity throughna range between maximum output and, substan tially zero output.

:Another object is to provide such ajcontrol means capable oibeing'actuated-by vacuum in the intake manifold of an internal combustion engine employed for driving-the pump to auto I 5Fig.;.5 .iska'horizontal zsectional' view of the U vacuumecontrolling valve device of my control apparatus'with'certain' parts thereof shown in one; position in fulllines and in another position While my pump control Iapparatusis adapted for ,useiiiwith fluid. pumps for various purposes it is particularly adaptedzforuse in automotive vehicle's having .a hydraulic propulsion system.

Referringtothe drawing Fig.1 shows an embodiment of myinventio'n'; The pump shown includes a casing C, .a fluid inlet connection or. conduit.;A,La fluid; Ol1t18tx00111180ti01'1 or conduit 13, andashaft'ZZ"fordriving a pump. Fig. 2 shows iniassimplified manner the pump identifiedigby the, letter C-and ..a'n engine E having a power matically vary the capacity 'of the pump'in pro-'- portion to variation in said vacuum.

Still another object is to provide such con trol-means with additional control facilities for selectively limiting the maximum capacityfor which the pump trol means. i I Yet another object is 'to providesuch pump control apparatus including still another con- 7 trol device for use to reduce the pump output to may be adjusted'by saidconoutputgshaft .24 connected through coupling means 237tdthedriving shaft or power input shaft-.Hioflthe pump C.;' The engine E is of the internalgcombustion type having an intakemani-I; fold 525::which-is. connected to my pump control apparatus for-purposes of control thereof. The inlet andoutletconduits A and B of the pump 0 are connected to "one orjmore fluid motorsM which. may beconnected-tb ;the wheels of a ve- 1 hicle ,for use in imparting driving torque thereto.

substantially zero independently of all other con- 7 trol means;

Another object is to providesuch pump con-- trol means adapted for operationby control elements similar to. thepedaletvith which auto? motive vehicles are customarily equipped.

A further object'is to'provide control means. 1 I

of light, simple, compact, eflicient, rugged and inexpensive construction;

.These and other objects and. advantagesof theinvention will more 'fully appear from the following description madein connection with .the accompanying idrawing, whereinlike ref erence characters refer tofthe same or :similar" parts, and iniwhich:

.Fig. 1 is a general top view of anadjustable ReferringztoFig. 1 the casing'of the pumpC includes-a relatively long cylindrical body 26, a

relativelyshort cylindrical body 21,.anend wall 28,:and -;a circularplate 29. Theshorter-cylindrical body- 21=is aligned with oneend of the longercyljindrical.zbody 26 andffthe plate 29 is placedqbetween-"thecylindrical bodies 26 and 21.

The end wall 28 is placed on the remaining end ofthe-longer cylindrical body26. ;The end wall 28,;the;body;26, .theplategZS, and'the body 21. are

held together ;by meansqof nutted bolts 30 so that they are sealed'to one'another and together form a"-r igidgenerally; cylindrical pump housing or a casing Thegportions;of thebodies:26 and 2'! adjoining' each other 1816 increased in diameter to form 321111111121 outwardly projecting members ,ZBband 21b,

Thedrive shaft 220i my pump is disposedfcocapacity pump'andan embodiment-of mycontrol-apparatus included as a portion thereof;

-Fig. '2 is a simplified side view of an, engine,

pump and a fluid motor suitable for'operative association of my, controlcapparatustherewith;

Fig. 3 is a horizontal longitudinal sectional view of the pneumaticshifting device. of my"con-.

trol apparatus axially: of the casing :C and extends longitudinallyl thereof; iroma"point outwardlyof the exteriorlyrdisposed end, of the cylindrical body 2! tea centrally located point toward the innerside ofthe endwall 28 I "Means operable froma point located exteriorly of the pump C is..provided for shifting. internal fparts' ofitheopumpCfor varying the capacity thereof. ".Three z shifting elements B8 'fdispos'ed parallel to each other project outwardly of the pump C through suitable apertures in the end wall 28. For cooperating with each of the shifting elements 68, a sealing means 66 is provided for each thereof for sealing the same to the end wall 28 of the Pump C. Since the pump C and the sealing means 66 include no structure therewithin constituting a part of the invention residing in my pump control apparatus, the internal construction of these devices need not be described or illustrated in this application.

Immediately to the left of the shifting elements 68 a yoke 69 is provided and the elements 68 extend through and are secured in suitable respective apertured portions of the yoke 69. The elements 68 are screw-threaded at their left-hand ends and nuts 18 are applied to the screw-threaded ends of the elements 88. A single operating rod H for moving the yoke 69 is provided. The rod H is externally screw-threaded in a portion of it disposed in the immediate vicinity .of the yoke 69, and is screw-threadedly engaged in a suitable centrally located internally screw-threaded apertured portion of the yoke 69. To the left of the yoke 69 a washer I2 is placed on the operating rod H. To the left of the washer 12 a nut 13 is provided on the operating rod I l. The nut 13 is provided to lock the rod H in any desired screw-threadedly adjusted position of the same relative to the yoke89.

Referring to Figs. 1 and 3 of the drawing a pneumatically operable device G is provided for moving the operating rod H for the purpose of varying the capacity of the pump C. The device G consists of a piston accommodating cylinder M closed at its rear end by a plate secured to a flange Ma on the cylinder 14 by suitable means such as the screws 18. The closure plate 15 is centrally apertured and a headed screw 11 extends outwardly through the apertured portion of the plate 15 with the head of the screw disposed at the inner side of the plate 15. Immediately outwardly of the plate 15 a. nut 18 is placed on the screw 1! to rigidly secure the same to the plate 15. The screw I1 is flattened and apertured in its free end portion and in this portion is connected by means of a pivot bolt 19 to a bracket 89 carried by a portion 8| of the frame of the vehicle in which the pump C is installed. The forward end of the cylinder 14 is provided with a closure wall Mb carrying on its outer side a centrally located boss [40, the bossed portion of the wall 14?) being centrally apertured and having a piston rod 82 extending therethrough. The inner end 82a of the piston rod 82 is of reduced diameter to form a shoulder and is screwthreaded. A pair of disks 83 and 84 are centrally apertured and are carried on the inner end portion 820. of the piston rod 82. The disks 83 and 84 are secured to the screw-threaded portion of the piston rod 82 by a nut 85 screw-threadedly mounted on the threads of'the portion 821:. of the piston rod 82. At their marginal portions the disks 83 are flared away from each other to form an annular groove of triangular cross-section. The annular groove carries therein an annular sealing member 88 formed of relatively flexible and compressible material. A helical compression spring 81 is placed within the interior of the cylinder 14 and. bears at its respective ends against the closure plate 15 and the disk 84. The normal position of the piston formed by the disks 83 and 84 and the sealing ring 86 will then be substantially as shown in Fig. 3; that is, closely adjacent the end wall 14b of the cylinder 14. A

portion 14d of the cylinder '14 adjacent the closure plate 15 is thickened and is formed at its outer side into a flat surface. A port 88 is provided by forming an aperture through the thickened portion 14d for the purpose of enabling communication with the interior of the cylinder 14. When the port 88 is connected to a source of Vacuum the piston of the operating device G will be shifted to the left as viewed in Fig. 3 against the pressure of the spring 81. This movement of the piston will, of course, result in increasing the output of the pump.

Means is provided connecting the piston rod 82 to the operating rod ll of the pump in axially aligned relation therewith. The free end portion 82a of the piston rod 82 is externally screwthreaded and carries thereon a nut 89. An apertured end of a bar 98 is placed on the threaded portion 82a of the piston rod 82 immediately outwardly of the nut 89. Outwardly of the bar an element 9| which is both internally and externally screw-threaded is screwed on to'the piston rod 82 in tightened relation with the bar 90 and the nut 89. The free end of the previously described operating rod H is formed into a ball 92. A cup 93 screwed on to the element 9| at its open end is provided'with. an aperture at its remaining end through which the operating rod H extends with the ball 92. disposed within the interior of the cup 93. To the left of the ball 92' as viewed in Fig. 4 is an element 94 having a recess inits right-hand side conforming to the contour of the ball 92. The element 94 is of such diameter as to fit within the cup 93 in the manner of a piston. The element 94.has a reduced diameter portion 94a projecting toward the free end of the piston rod 82 and spaced therefrom but a slight distance. A helical compression spring 95 is interposed between the element 94 and the element 9| so as to maintain the element 94 in spring-urged engagement with the left-hand side of the ball 92. The ball 92 and the parts associated therewith comprise a ball and socket joint. For lubrication of the ball and socket joint thus formed an oil hole 96 is formed in the wall of the cup 93 as shown.

For control of communication between the port 88 of the pneumatic operating device G and a source of vacuum such as the intake manifold 25 of the engine E, I provide valve apparatus H such as shown in Fig. 5. The device H consists of a body 91 having a projecting portion 91a carrying an apertured flange 91b which is secured to the flat exterior surface of the cylinder 14 of the device G by suitable means such as the cap screws 98. The body 91 has therewithin a pair of parallel elongated bores 91c and 91d. The bores 97c and 91d are of cylindrical shape and extend from the left-hand (as viewed in Fig. 5) end of the body 2'! to points closely adjacent the right-hand limit of the body 91. The bore 910 is disposed closer than the bore 91d to the neck 91a of the body 91. The body 91 is provided with a passage 99 therethrough registeringwith the port 88 of the device G and extending through the body 91 to diametrically intersect first the bore 910 and then the bore 91d. The outer end of the passage 99 is provided with a connection fitting [90 to which a tube l9l leading from the intake manifold 25 of the engine E may be connected by means of a connecting element I92. An elongated cylindrical element I03 is disposed in the first bore 910 in'closely fitting but longitudinal sliding relation thereto. At its righthand end the element I03 has a portion |93a of ;redu ced diameter projecting outwardly of ,the body 9fl through an aperture -;I04 ":formed inlthe right-hand jend -f zthe-body 9l coaxially :of the bore 1937c iandjhavingpza diameter :somewhat in excess of athe -diameteraof the outwardly, project'- inggreduced portion 103a ofqthe element I03. The

shoulder provided at the jjunctionrbetween the fullgdiameter portionof the element I03 and the vreduced diameter portion 103a acts as astop engageable with portionsof the :body 9-! bordering the aperture I04 for the purpose of determining the right-hand limit of movement-of the element I03. The left-hand end of the bore 1910 is provided with a plug I05 screw-threadedly engaged in-internal screw-threads formed in the left-hand end of the portion of the body9'l 'defining'the bore 91c. A helical poinpressionspring I05a is interposedqbetween the plug I05 and the left-hand endof the element I03 for the purpose of yieldably urging the element I03 toward its righthand limit-Of movement. The element I03 has therein an annular groove 10% so located relative to the length of theelement I03 as-to be aligned with the passage 99 when the element I 03 is at :its right-hand limit of movement Ad joining the groove I03b at the right-handfside 7 thereof a portion I030 of the element I03 having a length approximately equal to the diameter of the passage 99 is ungrooved to act as a valve for partially blocking flow of air through the passage ;99;whensaid ungrooved portion I030 is andkis s cured; in -the aperture by means, of a {set screw .jI08. A oentrallygapertured plug I09 is screw-.th-readedlygmounted in the left-hand, end ofxthe;portion of the body,;9I; defining the bore.

91d. The wire-I101 extends outwardly of the body 9 through the aperturedlplug I09; :-A casing :I I0 for the controliwire :I 011s received in an'enlarged outeriportion of the aperture in the plug I09 and secured-therein by means of a set screw II-I. The-controlwire IIEI and the casing I-I0 therefor'may be extendedvto any desired suitable type ofacontrol element manipulatable by the operator ofithe vehicle-in which my pump is incorporated.

This :controlmeans isused for the purpose of,'enabl-ing-the operator tofsetgthe pump for minimum output regardless oftheposition in which the v'a1ve-e1en'1entI03 mayhappen to' be disposed. I i prefer that-the control wire I01 be connectedtoj.

the rodbeing extended through an aperturein the free end of the bar 90 which is carried by the placed in registry with the passage 99. ,Ob-

viously when the element IE3 is shifted to its right-hand limit of movement the annular groove I-03b serves to conduct air 7 between portions-of of. From the right-handlimit of the ungrooved portion I03c of the element I03 to the righthand end ,of thefull diameter portion of ,the' ele'-' ment I03 a longitudinally extending groove I03d is formed in the element I03 in theside thereof nearest the pneumatic device G'. The groove I03d 1 serves to permit admission of air through the aperture I04 and the groove I03d into thecylinder. I4 of the deviceG when the element I03 is shifted to a position slightly to; the left of" the position in which it is shown in Fig. 5.

'35 the passage99 disposed at opposite sidestherfen The right-hand end of the bore 91d is providedwith a small air admitting aperture 91) through the right-hand end of the body 91. Within the bore 91d there is provided a somewaht elongated cylindrical element I06 closely but longitudinally slidably fitting the portions of the v 7 body 91 defining the bore91d. The element I06 has near the left-hand end thereof. an annular groove I06a for permitting passage of air between portions of the passage 99 at opposite sides thereof when the element I06 is in the position I shown in Fig.5. To the right of the groove I06a the element I06 is ungrooved through an axial. distance approximately equal to the diameterofthepassage 99 so that the passage 99 will-be blocked when said ungrooved portion is'in regis trytherewith. To the right of the ungrooved portion of the element I00 a longitudinally extending groove I066 is formed in the side of the element I00 nearest the previously. described elongated element I03. The groove I05?) is for the purpose of admitting air through the. aperture 91 the bore 97dand the groove I06b' into the passage 99 when the element I06 is so positioned that the groove I06bis in communication with the passage 99. For operation of the valve element I06 a control wire I0'I is received in a suitable aperture in the element I06 as shown tor of a vehicle in which my apparatus isfiin- 1 corporated tojshift the Wire II5 longitudinally of the casing; H4 and hold-the wire H5 in'any piston rod 82 of the pneumatic devioe G. The -bar. is-movable longitudinally of the rod I I2 responsive to the longitudinalmovement of the control rod II of the pump. The outer end por-- tion of the cylindrical valve element I03 is shouldered at I-03e and provided with screw-threads I-03f-outwardly of the shoulder I03e, Aflat member II3 Whichxisvapertured in its medial portion andmounted in its apertured portion onarod II 2 for lsliding movement longitudinally thereof is aperturedjat its lower end as viewed in-Fig. b and is mounted on the screw-threaded portion I0-3f :of'the valve element, I03. .The flat member II3 is secured .tothe outerportion of the, valve element I03 :by means of a nut H4. Thevupper end of the fiat member, -I-I3 as viewed inFig. 5

carries a socket member 3:: wherein a flexible.

casing l I4 containing a control wire Ilfiis vseouredby means suchas the set screw I Ma. 7 The flat member] I3 is apertured'for extension of the control wire I I-5 the'rethrough toward the, bar, 90.-

Anabutment element II6 is mounted on thekrod 2 for longitudinal movementetherealong between 'the flat/member II 3 and-the: bar 90 and the end of the wire I I 5 is secured to the element IIS; by "means such as u-the set screw 40,;

' The control wire H5 and casing "H4 .maybe: 2 extended to and connected to any suitable co'n-f trol'elernent adapted for operationby the opera- ,jadj usted longitudinally shifted relation with the flexible casing II4. This control element may be similar tothe-wjell known frictionally restrained button control 'device which is commonly-usedin nearly all present day automobiles as a hand throttle or choke control device orsimilarto'well known -hand control pull button devices which have been widely used tocOntrol radiator :shutters, mufiler cut-out valves and other devices througha-pull wire in afiexible casing., Manipulatio'n of the; control ,wire I I5 to shift the sarner 1 longitudinally of the casing H4 is utilized to" e-ffect, adjusti-ve variation'in the distance between the fiat member vI I3; and -theabutment {element projecting H6. The casing H4, being flexible, will move, at the corresponding end thereof with the flat member H3 to accommodate said shifting and variation. When the wire H is held in an adjusted longitudinally shifted relation with the casing H4, the distance between the abutment element in which the wire I I5 is secured and the flat member H3 in which the casing H4 is secured is adjustively fixed since the wire I I5 is of such strength as to prevent stretching or buckling of the portion thereof extending through said distance and the wire H5 is retrained against longitudinal movement in the flexible casing I I4. As the flat member H3 moves relative to the valve body 91 the flexible casing I I4 and the wire H5 therewithin will bend together as a unit in portions thereof immediately to the left of the flat member H3. As the operating rod II is moved to the left to increase the output of the pump the bar 96 will be moved therewith to the left, as for example from the dotted line position shown in Fig. 5 to the full line position. The bar 90; functions as an abutment for element I I 6. When the bar 90 has engaged the abutment element I IS, the abutment element I I6 will move with the bar 90 as the bar 90 is moved still further to the left. During the last mentioned movement the leftward movement of the abutment element H6 is transmitted through the control wire H5 and casing IM to the flat member H3 and to the valve element Hi3. Movement of the valve element I63 to the left will first block communication between the connection element Hill and the interior of the cylinder I4 of the pneumatic operating device G. This will prevent further movement of the piston rod 82' to the left. If the valve element N13 is moved sufficiently to the left the groove I83d therein will conduct air to the passage QS and from the same into the cylinder I5 to admit air thereto, and accordingly permit the spring 82' to push the piston rod 82 to the right for reducing the capacity of the pump. In the position shown in Fig. 3 it will be noted that there is a slight degree of communication between air passage H336! and passage 99. Initial movement of the piston 33 causes movement of the valve I63 to the position shown in Fig. 5. The slight flow communication between said passages 13d and 951 permits flow of air into the chamber G to increase pressure therein and permit further movement of the piston 38 slightly to the right. This will move the valve I03 to a position where a degree of communication is afforded from air passage 99 through air passage 13d to the conduit I90 which is connected to the source of reduced pressure. This variation of the valve I03 due to pressure changes will result in an approximate balance and a slight degree of communication will still be afforded between air passage IBM and passage 99. A drop in applied suction permits the bleeding of air from passage 13d through passage 99 to the left-hand side of piston 83. A helical compression spring Ill is placed on the rod H2 between the flat member H3 and the portion 9'Ie of the body 91. The purpose of this spring H1 is to afford yielding resistance to leftward movement of the flat member H3 beyond the point where the air admitting groove I03d of the valve element I83 comes into communication with thepassage 85 The abutment member 99 and abutment element H6 operate cooperatively in such a manner that the valve I53 will be operated to prevent movement of the control rod 'II to the left appreciably beyond a point where the abutment member engages the abutment element H6. It then follows that the control wire H5 may be adjustively operated to adjustively determine the maximum output of the pump. For example, when it is desired to start a vehicle having my pump incorporated therein in association with an engine E and wheel driving motors M, the control wire H5 may be projected to such a distance that the pump will have a minimum output per revolution and hence produce a transmission ratio between the engine E and wheels driven by the motors M corresponding to the transmission ratio obtained in the conventional motor vehicle when the gears are placed in what is commonly known as low gear. As the vehicle starts to move and increase its speed of movement the wire H5 may be retracted to permit successively higher outputs of the pump to change the transmission ratio between the engine E and wheels driven by the motors M toward a ratio corresponding to that obtained in the conventional motor vehicle when the transmission gears thereof are set in what is commonly known as high gear.

The output of the pump is also varied responsive to changes in the degree of vacuum existing in the intake manifold 25. This output variation obtained responsive to variation in manifold vacuum is such as to automatically decrease the output of the pump responsive to increased load such as would be occasioned by a vehicle reaching and ascending a hill. The reduction in output of the pump, of course, produces a change in transmission ratio such that the engine E will produce a greater number of revolutions than before relative to the number of revolutions of the motor M. The manner in which this variation in transmission ratio is effected is as follows. The variable device H is first assumed to be in such condition that the interior of the cylinder I4 of the pneumatic device G is in communication with the intake manifold 25 and will hence have therewithin a degree of vacuum corresponding to the degree of vacuum in the intake manifold 25. As the vehicle encounters a hill the torque required from the motor M and hence the torque developed by the engine E is increased. This will cause a reduction in the degree of vacuum in the manifold 25 and in the cylinder I4. Reduction in vacuum will enable the spring 81 to push the piston rod 82 to the right to such a point that the pressure of the spring 81 will be equal to the pull of the vacuum on the piston of the device G. This movement of the piston 84 to the right results in reduction of the output of the pump C, and accordingly alters the transmission ratio to provide a greater mechanical advantage between the engine E and the wheels driven by the motors M. When the vehicle proceeds from an upward slope on to a level road the vacuum in the manifold 25 and in the cylinder I4 will tend to increase due to reduction in the torque required of the engine E. This increase in vacuum will suck the piston of the device G to the left until the suction on the piston equals the pressure afforded by the spring 87. This leftward movement, of course, increases the output of the pump and reduces the number of revolutions of the engine E relative to the revolutions of the wheels of the vehicle. The engine E may, of course, be provided with a throttle of conventional type and provided with a throttle control accessible to the operator of the vehicle. With my automatic control it should be apparent that less variation in throttle position will be required than is necessary in operation of conventional motor vehicles when the road conditions vary.

I For the purpose of excluding dust a cover H8 which may be formed, if desired, or flexible ma-' terialfand be in tubular form is placed on the I casing Caof the pump at one end and on the device G and H at its other end. A supporting ring for the medial portion of the dust shield I I8 may be provided if desired and this ring H9 may be rigidly attached to any convenient means of support. I

For convenient operation of the control wire -|l Ipreferthat the same be connected to a pedal corresponding in nature and location to the usual clutch pedal of conventional motor paratus for variable capacity fluid pumps wherein particularly effective automatic controlmeans are included. I

rangement and proportions of the various parts I without departing from the scope of my inven tion, which generally stated,.oonsists in the mat-- ter shown and described and set forth in the appended claims. a

What is claimed is:

1. Positioning apparatus consisting of, the combination of a pneumatic device having a shiftable element carrying a control member, said shiftable element being associated with a chamber so as to be deflected in one direction responsive to vacuum produced in said chamber, resilientfmeans yieldably urging said shiftable elementin the opposite direction, valve means for controlling communication between said chamber and a source of vacuum, resilient means for yiel-dably holding said valve open relative to said communication, a shiftable operating member for said valve having an abutment element carried thereby, and an abutment member carried by said control member and aligned with said abutposite direction being included in said pneumatic device, valve means for controlling communica- It will, of courseQbe understood that various changes may be made in the form, details, ar-

vber to the atmosphere when in a closed-position relative to said communication between said chamber and a source of vacuum. I l V 2. Positioning apparatus consisting of, the combination of a pneumatic device having a shiftable element carrying a control member,

said element being associated with a chamber so as to-be defiectiblein one direction responsive to vacuum produced in said chamber, resilient means yieldingly urging said element in the 0ption between said chamber and a source of vacuum and including two valvesconnectedin series, each ofsaid valves being arranged to connect said chamber to the atmosphere when in fully closed position relative to said communication, resilient meansfor yieldably holding one of said' valves open relative to said communica tion, a shiftable operating member for said one valve having an abutment element carried the'rea -by, and an abutment'member connected with said control ,member to shift therewith and aligned with said abutment element for engaging the same to cause closure of said one .valve relative to said communication at ,a predetermined point inshifting movement of said shiftable ele- I ment in said one direction to halt said'movement at said point, the second of said valves being arranged -for manual'operation thereof.

3. Positioning apparatus consisting of, the

combination of a pneumatic device having a shiftable element. carrying a control member,

said element being associated with a chamber so as to be deflectiblein one direction responsive to vacuumproduced in said chamber, resilient means yieldingly, urging said elementin the opposite direction being included in said pneumatic device, a valve for controlling communicationbetween said chamber'and a source of vacuum, resilient means for'yieldably holding said valve open relative to said communication,

' a shiftable operating member-for said valve havmg an abutment element carried thereby, and ,an abutment element connected with said control member to shift therewith andaligned with said first mentioned abutment element for engaging'the same to cause closure of said valve relative to, said communication at a predetermined'point in movement of said shiftableele- I ment insaid one directionto "halt said movement element for engaging the same to cause;

closure of said valverelative to said communication at a pre-determined point in movement of said shiftable element in said onedirection so as to halt said movement at said point, and,

said valve being arranged to connect said chamment at said oint, one of said abutment-ele- 'ments being adjustively movable relative to the corresponding one of said members in the direction of relative movement of said abutment elements to enable selective variation of the position of said predetermined point.

' HERBERT J. NATHAN. 

